This invention relates to a method of and means for producing combustible gases from solid fuel such as low grade solid fuel for example oil shale and/or the like and more particularly to a method of and means for supplying solid material using a screw conveyor.
Oil shale is found throughout the world and would constitute a plentiful and relatively inexpensive fuel if techniques were available for quickly and inexpensively processing the oil shale into combustible gases. One approach to processing oil shale into combustible gases is disclosed in U.S. Pat. No. 4,211,606 (the disclosure of which is hereby incorporated by reference). In this patent, oil shale is heated in a dryer using clean, hot flue gases producing heated shale that is applied to a pyrolyzer or reactor. The heated shale is further heated in the pyrolyzer with hot ash to produce combustible products, and carbonaceous material that is added to a gasifier. Hot gases and steam are applied to the gasifier such that combustible gases are produced. The residue of the gasifier is extracted and applied to what the patent terms an air jet furnace, details of which are disclosed in U.S. Pat. No. 4,110,064 the disclosure of which is also incorporated by reference.
The air jet furnace produces combustion products in the form of hot flue gases whose major constituents are nitrogen, carbon dioxide and particulates which are applied to a separator which separates the combustion products into a stream of hot coarse ash, portion of which is supplied to the pyrolyzer and another portion of which is disposed of, and a stream of hot gas containing fine ash. The stream of hot gas and fine ash is applied to a separator that produces a stream of fine ash that is applied to the gasifier, and a stream of gases containing residual ash. The latter stream is applied to a further separator that produces the clean flue gases that serve to heat the shale in the dryer.
A less complex derivative of the apparatus described above has apparently been used in two plants in the U.S.S.R. in 1990 and 1991. As presently understood, the actual design eliminates the gasifier and the dryer. Oil shale is fed into a pyrolyzer wherein pyrolyzation takes place producing carbonaceous material after a predetermined residence time of the shale in the pyrolyzer. This material is supplied to an air jet furnace wherein combustion takes place producing hot flue gases, and particulates that are applied to a separator which separates the flow into a stream of coarse ash, and a stream of hot flue gases containing fine ash, such as fly ash. The stream containing the hot coarse ash is applied to the pyrolyzer which produces pyrolysis gas at a temperature in excess of 400xc2x0 C. Such gas contains combustible products, steam and carbon compounds. The stream containing the combustible products from the pyrolyzer is applied, together with the stream of hot flue gases containing fine ash to a burner that is part of a combustion chamber of a boiler that produces steam that may be used for generating electricity.
One of the problems with such systems is the conveyor or feeder which are used for supplying the carbonaceous material from the pyrolyzer to the furnace. Furthermore, such conveyors would also be problematic were they used for supplying carbonaceous material from the pyrolyzer to the gasifier and material from the gasifier to the furnace in systems operating in accordance with U.S. Pat. No. 4,211,606. Firstly, the temperature of the carbonaceous material is reasonably high, approximately 400xc2x0 C. or more. Such high temperatures cause problems including thermal expansion. Secondly, when screw conveyors are used, they are known to suffer from lateral movement. Thirdly, a constant and steady feed of the hot carbonaceous material has to be ensured in order, among other things to assure that any back pressure from gases flowing in the furnace does not cause combustion or high temperatures in the conveyor. Furthermore, the bearings of the motor which operates the conveyor is prone to wear and tear. In addition, such systems suffer from a reduction in thermal efficiency and available power caused by fouling of the heat transfer in the steam boiler of the power plant due to the entry of fly ash into the boiler and by carbonate decomposition. Also such systems are usually designed to operate on a certain oil shale and cannot be easily converted for use with another oil shale. Additionally, these systems are suited for operation with oil shale having a relatively high calorific value (eg. above 2,000 kcal/kg) and are not actually suitable for use with oil shales having a very low calorific value (eg. 700 kcal/kg).
It is therefore an object of the present invention to provide a new and improved method of and means for producing combustible gases from solid fuel such as low grade solid fuel for example oil shale and/or the like which substantially overcomes or significantly reduces the disadvantages outlined above.
In accordance with present invention, a method for supplying solid material such as hot carbonaceous material from a pyrolyzer or reactor to a furnace, is provided comprising providing a screw conveyor for receiving the solid carbonaceous material from the pyrolyzer or reactor preferably from above the conveyor and transporting it along its length to a vaned rotor preferably positioned on the axle of the screw conveyor preferably substantially near the end of the screw conveyor for supplying the carbonaceous material to the furnace.
The rotor has a substantially horizontal, side exit chute positioned substantially near the rotor for transporting the solid carbonaceous material from the vaned rotor to the furnace such that the carbonaceous material is moved substantially tangentially to the axis of rotation of the screw conveyor and thus extracted substantially horizontally and perpendicular to the axis of rotation of the screw conveyor. Preferably, the chute is slightly upwardly inclined to the horizontal such that the carbonaceous material accumulates and produces a plug of material at the exit chute. Furthermore, the chute is preferably positioned at the lower portion of the rotor where usually most of the carbonaceous material is found. Also preferably, the chute is provided with an expansion joint advantageously including a ball joint to give the chute flexibility.
In addition, two bearings are provided, one at each end of the screw conveyor for supporting the axle of the conveyor. Furthermore, the chute is preferably provided with a substantially vertically maneuverable, hinged and preferably length adjustable extension such that when the chute is connected to the furnace, the hinged flat is present in the furnace. Positioning this extension at a certain angle to the horizontal and preferably setting its length also permits carbonaceous material to accumulate at the exit chute producing a plug of material such that the flow of gases present in the furnace into the chute and the screw conveyor is minimized. If preferred, a plate or pair of plates positioned adjacent the rotor and in the upper portion of the conveyor housing can be provided for further minimizing the possibility of gases present in the furnace to enter into and flow along the screw conveyor.
According to the present invention, apparatus is also provided for supplying solid material such as carbonaceous material from a pyrolyzer or reactor to a furnace comprising a screw conveyor for receiving the solid carbonaceous material from the pyrolyzer or reactor preferably from above the conveyor and transporting it along its length to a vaned rotor positioned preferably on the axle of the screw conveyor preferably substantially near the end of the screw conveyor for supplying the carbonaceous material to the furnace. The apparatus also is provided with a substantially horizontal, side exit chute, which is preferably slightly upwardly inclined to the horizontal, and positioned substantially near the rotor for transporting the solid carbonaceous material from the vaned rotor to the furnace such that the carbonaceous material is moved substantially tangentially to the axis of rotation of the screw conveyor and extracted from the screw conveyor substantially horizontally and perpendicular to the axis of rotation of the screw conveyor. Consequently, the carbonaceous material accumulates and produces a plug of material at the exit chute. Furthermore, the chute is preferably positioned at the lower portion of the rotor where usually most of the carbonaceous material is found. Also preferably, the chute is provided with an expansion joint which advantageously comprises a ball joint for providing flexibility to the chute.
In addition, two bearings are provided, one at each end of the screw conveyor, for supporting the axle of the conveyor. Furthermore, the chute is preferably provided with a substantially vertically maneuverable, hinged preferably length adjustable extension such that when the chute is connected to the furnace, the hinged extension is present in the furnace. Thus, by maneuvering the extension and setting it at a certain angle as well as preferably setting its length, the extension also permits carbonaceous material to accumulate at the exit chute to produce a plug of material which minimizes the flow of gases from the furnace, in which a higher pressure usually prevails, into the chute and the screw conveyor. If preferred, a plate or pair of plates positioned adjacent the rotor and in the upper portion of the conveyor housing can be provided for further minimizing the possibility of gases present in the furnace- to- enter- into and flow along the screw conveyor.
By using a vaned rotor positioned preferably on the axle of the screw conveyor to supply the carbonaceous material to the furnace, a constant and steady feed of the hot carbonaceous material exiting the conveyor is ensured, while the use a chute slightly inclined to the horizontal contributes to assuring the buildup of carbonaceous material at the chute. In such a manner, a plug of material is produced at the exit of the chute. In order to ensure this, the chute is preferably positioned at the lower portion of the rotor where usually most of the carbonaceous material is found. The plug of material produced minimizes the flow into the chute and screw conveyor of gases present in the furnace having a slightly higher pressure above air or gases found in the conveyor. In this regard, the preferably provided vertically maneuverable, hinged length adjustable extension additionally aids in producing the plug of material for minimizing the gas flow into the chute and screw conveyor from the furnace.
In addition, the provision of two bearings each supporting an end of the conveyor substantially reduces the lateral movement of the conveyor and wear and tear on the bearings were only one bearing used.
Preferably, the conveyor and rotor are made of heat resistant material in order to provide reliable operation in the high temperature range.
It is presently envisaged that a conveyor constructed and operated in accordance with present invention can be used for transporting virtually any solid material, particularly when the solid material is hot and/or where its outlet is present in an environment or location containing gases having a pressure higher than gases present in the conveyor. However, in what is presently considered to be the best mode for carrying out the present invention, the conveyor is preferably incorporated in a system for producing combustible gases from solid fuel such as low grade solid fuel for example oil shale and/or the like. In such a system, a pyrolyzer or reactor is used for pyrolyzing portion of the low grade solid fuel to produce combustible gases and carbonaceous material. The screw conveyor, preferably used, receives the hot solid carbonaceous material from the pyrolyzer, preferably from above the conveyor, and transports it along its length to the rotor positioned preferably on the axle of the screw conveyor preferably substantially near its end for supplying the carbonaceous material to the furnace. Means for adding a further portion of the solid fuel to the furnace are provided such that the carbonaceous material and the further portion of solid fuel are combusted in the furnace to produce combustion products that include hot flue gases and ash particulate. A separator separates the combustion products into a number of streams, one of which contains ash and the another of which contains flue gases and fine ash. Ash from the first mentioned stream is directed into said pyrolyzer.
The conveyor can also be used in a system for improving raw phosphates containing organic matter wherein the preferred system is analogous to the system described hereinbefore for producing combustible gases from low grade solid fuel.